The present invention relates to filter tube making, and more particularly to an apparatus and method for forming a flat paper strip into a tubular shape for subsequent use in the formation of cigarette filters.
U.S. Pat. Nos. 3,517,480 and 3,603,058 illustrate and describe machines for the production of composite cigarette filters by directly flowing granular filter material from a storage hopper into a vertically oriented paper filter tube. Similarly, US Patent Application Publication 2002/0119874A1 describes another machine for producing compound cigarette filters that includes a series of rotating plates with cavities therein into which the granular filter material is deposited. The cavities ultimately are aligned with an open ended paper filter tube to facilitate deposit of the granular material into the tube.
Preformed paper filter tubes are utilized with machinery as described above for primarily producing 2-up (dual) cigarette filters. In each instance these filter tubes primarily comprise a hollow cylindrical tube with a central filter component such as cellulose acetate tow. After both ends of the filter tube are filled with granular material and sealed with solid filter segments a 2-up (dual) filter is produced which when combined with tobacco rods at each end thereof ultimately produces two complete cigarettes. When cuffing through the middle of the central filter component, each cigarette filter has a defined length. It is important that the length and inside diameter of the preformed filter tube be accurately controlled so that the tubes can then be easily and accurately filled utilizing vertical filling technology and machinery of the type described above. Such filter tubes may also be filled utilizing horizontal filing technology.